Strict regulatory requirements govern process vessel and piping system cleanliness in many industries. In certain industries, such as the food processing industry, dairy industry, pharmaceutical industry, and the like, vessel and system cleaning must be performed regularly or daily to meet strict regulatory requirements. In addition, in these industries as well as others, vessels and piping systems may also require periodic cleaning to perform maintenance on the vessels or systems, or subsequent to performing maintenance thereon, prior to placing such systems into operation.
To meet such cleanliness requirements in the most effective and cost efficient manner, many facilities, and in particular processing facilities which require regular or daily cleaning, have installed "clean-in-place" systems. These systems are usually permanent, fixed, "hard-piped" systems which operate to clean process systems quickly and without temporary piping, hoses, pumps, and the like. Moveable equipment and vessels, such as those associated with tank trucks, are typically cleaned using hoses and other partially temporarily assembled systems.
Known clean-in-place systems typically comprise a number of tanks and associated pumps, automatic and manual valves, and interconnecting piping. The systems generally fall into two broad categories, namely, multiple use systems in which the chemical cleaning agent is stored after use and subsequently reused for system cleaning, and single use systems in which the chemical cleaning agent is used once and discarded after use.
Exemplary of the single use type system, is that system disclosed in U.S. Pat. No. 5,392,797 to Welch, which patent is commonly assigned with the present invention and is incorporated herein by reference.
In multiple use systems, often the final rinse solution from one cleaning cycle is stored and the solution is reused as an initial rinse solution in a subsequent cleaning cycle.
Single use systems can be configured as single tank or multi-tank systems. Such systems may include an eductor pump located at the clean-in-place unit to return the cleaning agent to the system or a motive pump return arrangement. An exemplary two tank eductor pump system includes a wash tank, a rinse tank, and a supply pump for supplying wash or rinse liquid to the vessel being washed. The two tank eductor pump system also includes a motive tank in addition to the wash and rinse tanks, and a motive pump to provide dynamic head for the eductor.
The motive supply tank of many such known systems typically has a large liquid surface area which is open to atmosphere to provide adequate surface area and opportunity for the returning solution to release any entrained air. Release of the entrained air in the returning solution is important to prevent air from entering with the feed solution to the motive pump. Air which may otherwise enter with the feed solution could cause the pump to lose prime or suction, and ultimately damage the pump.
In many of the known return systems, the return solution recirculates through the motive supply tank. Moreover, such tanks typically do not have provisions for cleaning, and, as a result, the tanks tend to retain soil and detrimentally transfer the soil to the wash solution later in the cleaning cycle. Other known systems include a spray device installed in the motive tank to clean the tank by use of, and during, an auxiliary cycle.
An exemplary two tank return pump system includes a wash tank, a rinse tank, a supply pump, and return pump. The supply pump supplies the wash or rinse liquid to the vessel to be cleaned and the return pump returns the contaminated liquid from the vessel to the clean-in-place system. Return pump systems are more prevalent in those industries which use clean-in-place systems.
In many such known return pump systems, solution is not completely removed from the vessel to be cleaned, and thus is not fully returned to the cleaning system. In an ideal arrangement, the vessel which is being cleaned should be kept free of standing liquid during the rinse and cleaning cycles to maximize the removal of soil and contaminating materials. However, in such systems, sufficient solution level must be maintained in the vessel in order to provide adequate prime for the pump. Thus, in such return pump systems, the solution level in the tank cannot be kept sufficiently low to maximize vessel cleaning. Moreover, after the return pump is stopped, some solution remains in the vessel. This remaining solution may carry into the next step of the clean-in-place cycle and effectively recontaminate the cleaned vessel.
Eductor pump systems, such as that disclosed in the aforementioned U.S. Patent to Welch, are effective in providing sufficient flow return from the vessel being cleaned. However, other problems may arise associated with the retention of soil in such motive tank systems.
Three tank systems are designed and operated similarly, except that, in general, the additional tank provides the ability to supply an acid or a caustic solution to the vessel, as required for a particular application. In some three tank systems, one of the hanks may be used to store the final rinse solution from a cleaning cycle to be used as the initial rinse for a subsequent cleaning cycle. In some known three tank system, a single wash solution is used, and the final rinse from one cycle is saved and used as an initial rinse for a subsequent cycle.
Clean-in-place systems are cost effective. Operating time for the clean-in-place system, and down-time for the process system are minimized because such clean-in-place systems are permanently installed to the processing system. Moreover, such clean-in-place systems provide superior results as compared to manual cleaning. Nevertheless, there are some disadvantages associated with presently used clean-in-place systems.
Additionally, operating costs for multi-tank clean-in-place systems can be high. Such operating costs include the cost of chemical cleaning agents which can be particularly high for systems which tend to dilute or lose cleaning agent inventory. Moreover, the loss of solution due to ineffective return flow can significantly increase the cost of operating such systems.
In addition, as previously discussed, known clean-in-place systems do not provide a low cost, effective method for increasing the quality of the return solution. As discussed above, there are problems associated with soil retention within motive pump systems, which may later be transferred to the vessel being cleaned when switching from the rinse mode to the cleaning mode.
Thus, there continues to be a need for a return pump system for use with clean-in-place system which return pump system allows for the release of large amounts of air from the recirculation loop, while returning high quality solution to the system for later use, and which is self-cleaning. Such return pump system minimizes the amount of standing water in the vessel to be cleaned, thereby cleaning the vessel in a cost efficient and sanitarily effective manner, and retains a minimum amount of such soil within the components of the system needed for cleaning the vessel, when switching from a rinse mode to a cleaning mode of operation.